[Physics] Some questions
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1. Why can birds stand on an overhead transmission cable without suffering any harm such as electrocution?
I have the answer as there is no p.d. between their feet, but why?
2. Why are overhead transmission cables found up high in the sky?
Other than the stupid answer "so no one can touch it", well, silly, I can put underground too so that no one can also touch it right. Somemore got ground insulation as well. "Double protection" heh.
My reason: Reduce heating effect of current flowing in cables so that power loss is reduced to the minimum. Temperature at a higher altitude is lower (think effect of air pressure on temperature of air molecules)
Correct? Or am I missing something?
Thanks for any help! :D
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Maybe digging grounds would cost more than constructing poles and hanging the wires overhead. Financial reason also.
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Originally posted by secretliker:
Maybe digging grounds would cost more than constructing poles and hanging the wires overhead. Financial reason also.
Then why do underground train stations exist?
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Originally posted by Garrick_3658:
1. Why can birds stand on an overhead transmission cable without suffering any harm such as electrocution?
I have the answer as there is no p.d. between their feet, but why?
2. Why are overhead transmission cables found up high in the sky?
Other than the stupid answer "so no one can touch it", well, silly, I can put underground too so that no one can also touch it right. Somemore got ground insulation as well. "Double protection" heh.
My reason: Reduce heating effect of current flowing in cables so that power loss is reduced to the minimum. Temperature at a higher altitude is lower (think effect of air pressure on temperature of air molecules)
Correct? Or am I missing something?
Thanks for any help! :D
no p.d.
high up so won't obstruct other stuff
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1. When reaching the bird, the current has the 'choice' of either going through the next part of the wire without passing the bird or going to the next part of the wire while taking a 'detour' through the bird's body
My teacher uses the analogy that current 'prefers' going through the path with less resistance. Heh.Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.
I would post an illustration, but dunno where to host
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Originally posted by Zandermccoll:
1. When reaching the bird, the current has the 'choice' of either going through the next part of the wire without passing the bird or going to the next part of the wire while taking a 'detour' through the bird's body
My teacher uses the analogy that current 'prefers' going through the path with less resistance. Heh.Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.
I would post an illustration, but dunno where to host
Nonsense I would say. Try touching a transmission cable with your hands (or one hand).
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if you can touch it and earth yourself, you can get electrocuted.
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Originally posted by Zandermccoll:
1. When reaching the bird, the current has the 'choice' of either going through the next part of the wire without passing the bird or going to the next part of the wire while taking a 'detour' through the bird's body
My teacher uses the analogy that current 'prefers' going through the path with less resistance. Heh.Thus, the current does not pass through the bird, because it would be a path with higher resistance than if the current just went through the wire straight.
I would post an illustration, but dunno where to host
If your teacher really used the word 'choice', he/she deserves to be sacked for teaching the wrong things to students.
skythewood is right. There's no potential difference. A current only flows between 2 points if there's a potential difference between those 2 points. No potential difference means no current will flow between them.
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What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.
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Originally posted by Garrick_3658:
What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.
the p.d is very very small, close to zero.
illustration is illustration, i like the choice thingie...
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Originally posted by Garrick_3658:
What is meant by "no potential difference"? As in the p.d. between the two points are equal? I don't get it.
yes. When you touch the cable, you are actually earthed. So there is actually pd. You wont get striked by lightning when you are in air if i am not wrong.
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My reason: Reduce heating effect of current flowing in cables so that power loss is reduced to the minimum. Temperature at a higher altitude is lower (think effect of air pressure on temperature of air molecules)
There is already reduced power loss by using those cables.
Temperature at high altitude being lower actually means more power loss(more energy loss per unit time) Think it through.
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the p.d is very very small, close to zero.
illustration is illustration, i like the choice thingie...
Show me how. My only question is why there is no p.d.
yes. When you touch the cable, you are actually earthed. So there is actually pd. You wont get striked by lightning when you are in air if i am not wrong.
What about planes?
There is already reduced power loss by using those cables.
Temperature at high altitude being lower actually means more power loss(more energy loss per unit time) Think it through.
If you cool the cables down, they don't get heated up as much and thus less power loss, isn't it?
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Firstly, thermal energy is loss whether or not the temperature is high or low. Thermal energy is loss because of the heating action of the current. Since current flows, wire is heated and heat is lost.
Secondly, the environment temp being low actually means that there is more efficient heat loss.
Thirdly, efficiency has to do with per unit time. Thus power loss is more.
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Originally posted by davidche:
Firstly, thermal energy is loss whether or not the temperature is high or low. Thermal energy is loss because of the heating action of the current. Since current flows, wire is heated and heat is lost.
Secondly, the environment temp being low actually means that there is more efficient heat loss.
Thirdly, efficiency has to do with per unit time. Thus power loss is more.
Har?Thought cold wire = power loss because the metal atoms are closer together = more resistence? And also because the negative electrons are less able to resist the positive cations because they have less energy to overcome the bonds?
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Originally posted by Garrick_3658:
Show me how. My only question is why there is no p.d.
What about planes?
If you cool the cables down, they don't get heated up as much and thus less power loss, isn't it?
___________________________________________ wire
^ ^
(finger 1) (finger 2)p.d at finger 1 is maybe 10000, finger 2 is 1000.0001
so p.d. is very small.
the end
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Originally posted by SBS2601D:
Har?Thought cold wire = power loss because the metal atoms are closer together = more resistence? And also because the negative electrons are less able to resist the positive cations because they have less energy to overcome the bonds?
I hope you are joking because you sound totally incoherent and disoriented.
cold wire= power loss? whats the link here?
Electrons are negative. Technically, there is no negative electrons because all electrons are negative.
why need to resist cations?
whats up with overcoming the bonds?
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Originally posted by davidche:
I hope you are joking because you sound totally incoherent and disoriented.
cold wire= power loss? whats the link here?
Electrons are negative. Technically, there is no negative electrons because all electrons are negative.
why need to resist cations?
whats up with overcoming the bonds?
Erm.We know that resistence varies with temperature.....try arguing that.
Edit: In fact, I looked at your reasoning and went
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Originally posted by SBS2601D:
Erm.We know that resistence varies with temperature.....try arguing that.
try this...
if the temperature difference is bigger, the heat lost is more.
for example, a ice cube will not melt fast in an air con room, but melt very fast in the sun.
the resistance varies with temp stuff happens. but not by much.
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Originally posted by skythewood:
try this...
if the temperature difference is bigger, the heat lost is more.
for example, a ice cube will not melt fast in an air con room, but melt very fast in the sun.
the resistance varies with temp stuff happens. but not by much.
Gotcha.Guess I've given my physics all back.
So it is a factor....hmm.
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Originally posted by SBS2601D:
Erm.We know that resistence varies with temperature.....try arguing that.
Edit: In fact, I looked at your reasoning and went
.Eagle or some pro pls confirm if my reasoning is right or wrong. My stand is even if the wire feels cold, essentially heat is lost quicker. I am sure most ppl can understand this. After an exercise, you lose heat more in a cold room than in a hot room.
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Originally posted by SBS2601D:
Gotcha.Guess I've given my physics all back.
So it is a factor....hmm.
but not much of a factor bah.... how tall is the wires, like 100 metres?
it will be alot windy, but the temperature doesn't change that much.
another reason why build so high is because it has less chance of being earthed. it is both dangerous and wasteful if that happens, and probably will knock out the power supply too.
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Originally posted by davidche:
Eagle or some pro pls confirm if my reasoning is right or wrong. My stand is even if the wire feels cold, essentially heat is lost quicker. I am sure most ppl can understand this. After an exercise, you lose heat more in a cold room than in a hot room.
I was thinking.....True that to achieve thermal equilibrium, heat loss would be greater for a cold environment.....but why is there a need for that equilibrium?
So if the system does try to attain thermal equilibrium, then the system would draw energy from the cable. Hmm.
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Originally posted by SBS2601D:
Gotcha.Guess I've given my physics all back.
So it is a factor....hmm.
I think it is pretty evident. It seems that you are the last to have "guessed" that.
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Originally posted by SBS2601D:
I was thinking.....True that to achieve thermal equilibrium, heat loss would be greater for a cold environment.....but why is there a need for that equilibrium?
So if the system does try to attain thermal equilibrium, then the system would draw energy from the cable. Hmm.
why is there a need for thermal equilibrium?